Lignin-Based Hydrogels: Synthesis and Applications

Abstract

Polymers obtained from biomass are an interesting alternative to petro-based polymers due to their low cost of production, biocompatibility, and biodegradability. This is the case of lignin, which is the second most abundant biopolymer in plants. As a consequence, the exploitation of lignin for the production of new materials with improved properties is currently considered as one of the main challenging issues, especially for the paper industry. Regarding its chemical structure, lignin is a crosslinked polymer that contains many functional hydrophilic and active groups, such as hydroxyls, carbonyls and methoxyls, which provides a great potential to be employed in the synthesis of biodegradable hydrogels, materials that are recognized for their interesting applicability in biomedicine, soil and water treatment, and agriculture, among others. This work describes the main methods for the preparation of lignin-based hydrogels reported in the last years, based on the chemical and/or physical interaction with polymers widely used in hydrogels formulations. Furthermore, herein are also reviewed the current applications of lignin hydrogels as stimuli-responsive materials, flexible supercapacitors, and wearable electronics for biomedical and water remediation applications.

New Developments in Medical Applications of Hybrid Hydrogels Containing Natural Polymers

“…contain many different functional groups (hydroxyls, carboxyls, carbonyls and methoxyls) as active sites, in preparation of functional hydrogels both by physical crosslinking with hydrophilic polymers by H-bonding and also by, polymerization, copolymerization, ATRP and reversible addition-fragmentation transfer (RAFT) polymerization, chemical crosslinking, crosslinking grafted lignin and monomers etc. [436][437][438].…”

Cultivation of Mushrooms and Their Lignocellulolytic Enzyme Production Through the Utilization of Agro-Industrial Waste

“…Lignin is a rigid aromatic, amorphous and hydrophobic polymer that has been recognized as a highly branched polymer with a variety of functional groups, such as aliphatic, phenolic hydroxyls, carboxylic, carbonyl, and methoxyl groups. These functional groups give lignin a unique and very complex structure [16][17][18]. The nature of the lignin polymerization reactions results in the formation of a three dimensional, highly-branched, interlocking network of essentially infinite molecular weight.…”

“…The nature of the lignin polymerization reactions results in the formation of a three dimensional, highly-branched, interlocking network of essentially infinite molecular weight. Lignin composition and content are influenced by plant species and the environment [17,18].…”

Preface to Special Issue of ChemSusChem on Lignin Valorization: From Theory to Practice

“…Phenolation modification of lignin is usually favorable prior to preparing LPF resin because the resulting LPF resins possess desirable viscosity, low residual solids content, and low formaldehyde/phenol emission comparable to commercial PF resins in similar applications . Benefiting from the presence of hydrophilic functional groups, lignin can be used as a formulation polymer for hydrogel preparation, and the resulting products are applicable in the areas of agriculture, environmental pollution treatment, and biomedicine, and as stimuli‐responsive materials, flexible supercapacitors, and electronics, among others . The lignin‐hydrogel has different polymeric networks with diverse physical or chemical interactions in the hydrogel formulations .…”

“…Benefiting from the presence of hydrophilic functional groups, lignin can be used as a formulation polymer for hydrogel preparation, and the resulting products are applicable in the areas of agriculture, environmental pollution treatment, and biomedicine, and as stimuli‐responsive materials, flexible supercapacitors, and electronics, among others . The lignin‐hydrogel has different polymeric networks with diverse physical or chemical interactions in the hydrogel formulations . Further, lignin‐derived aerogel also exhibits a tremendous potential in the adsorption of liquid contaminants .…”